This invention relates to a heavy duty pneumatic radial tire used under a higher pressure and a higher load and suitable for construction vehicles mainly running on rough road, and more particularly to a heavy duty pneumatic radial tire capable of more improving the durability of the belt structure by arranging a high-strength belt comprised of at least one narrow-width slant cord layer between a crown portion of the known radial carcass and the known reinforcement belt for mitigating an action of a pressure applied from the radial carcass to the reinforcing belt accompanied with the expansion of the tire inflated under an air pressure.
The radial tire has a reinforcement belt comprised of wide-width rubberized slant cord layers for reinforcing a tread portion between a crown portion of a radial carcass and a tread rubber and developing so-called hoop effect and the like. And also, an inclination angle of the cord in each wide-width slant cord layer constituting the reinforcement belt with respect to an equatorial plane of the tire is usually set to be within a range of 20xcx9c40xc2x0 for causing so-called pantograph deformation between ply cords of the radial carcass in a product tire followed by size growth in vulcanization building or the like to develop the reinforcing effect and the like. Furthermore, it is common that at least two layers among the wide-width slant cord layers are so-called cross cord layers cords of these layers are crossed to each other with respect to the equatorial plane of the tire.
When an internal pressure is applied to the tire having the above belt structure by filling an air pressure, the radial carcass indicates a tendency of approaching to a circular contour at its section at a state of arranging no reinforcing belt or at a non-hooped state.
However, since the tire is hooped with the reinforcement belt, the section of the crown portion in the radial carcass at the inflation under the internal pressure has actually a radius of curvature larger than a radius of curvature in the circle. This is simply that the reinforcement belt controls the deformation in a direction of decreasing the radius of curvature for approaching to the circle or in a direction of growing the size at the tire section. Particularly, a pressure is applied to a widthwise central portion of the reinforcement belt accompanied with a force of increasing the carcass size. On the other hand, both widthwise end portions of the reinforcement belt indicate a tendency of separating outward from the radial carcass in the radial direction of the tire. In case of the tire having such both end portions of the reinforcement belt, the belt durability in the tire tends to be degrade by repeatedly subjecting the tire to a large deformation during the running under a load. This tendency becomes particularly remarkable in heavy duty radial tires used under a higher internal pressure and a higher load.
In JP-B-3-23361, JP-B-3-23362 and the like is disclosed, for example, that it is useful to apply a laminate of two narrow-width slant cord layers, cords of which layers being crossed with each other with respect to the equatorial plane of the tire between the crown portion of the radial carcass and the reinforcement belt as means for mitigating the action of the pressure applied from the radial carcass accompanied with the increase of tire size at the inflation under the internal pressure to the reinforcement belt and to arrange a high-strength belt wherein the inclination angle of these laminated cords with respect to the equatorial plane of the tire is made smaller than the inclination angle of the cord in the wide-width slant cord layers constituting the reinforcement belt in view of the prevention of degrading the belt durability.
Since the reinforcement belt elongates through shearing deformation at a ground contact surface of the tire during the running under a load owing to its properties, there is usually a tendency of creating strain between the wide-width slant cord layers constituting the reinforcement belt due to these shearing deformation and elongation to cause separation failure. The inventor has examined the belt durability in the tire having the belt structure disclosed in the above publications and elucidated that the tire having such a belt structure controls separation failure between the wide-width slant cord layers but tends to easily cause separation failure between the high-strength belt and the reinforcement belt, and particularly that when the difference of the inclination angle between the cord in the innermost wide-width slant cord layer constituting the reinforcement belt and the cord in the outermost narrow-width slant cord layer constituting the high-strength belt is not less than 10xc2x0, separation failure is apt to be remarkably caused between the high-strength belt and the reinforcement belt and the cord in either one of the innermost slant cord layer and the outermost slant cord layer is apt to be broken in the worst case.
For this end, the inventor has further made various studies in order to prevent the occurrence of separation failure between the high-strength belt and the reinforcement belt and found that the occurrence of separation failure between the high-strength belt and the reinforcement belt can effectively be prevented by rationalizing a gauge of rubber located between the cord in the innermost wide-width slant cord layer constituting the reinforcement belt and the cord in the outermost narrow-width slant cord layer constituting the high-strength belt.
And also, it has been elucidated that the problem similar to that between the high-strength belt and the reinforcement belt may be caused even between the innermost narrow-width slant cord layer constituting the high-strength belt and the carcass ply. Even in this case, it has been found that the occurrence of separation failure between the high-strength belt and the carcass ply can effectively be prevented by rationalizing a gauge of rubber located between the innermost narrow-width slant cord layer constituting the high-strength belt and the ply cord constituting the radial carcass.
It is, therefore, an object of the invention to provide a heavy duty radial tire used under a higher pressure and a higher load and suitable for construction vehicles mainly running on rough road wherein separation failure apt to be caused between high-strength belt and reinforcement belt is effectively prevented to improve belt durability by arranging a high-strength belt between a crown portion of a radial carcass and a reinforcement belt and rationalizing a gauge of rubber located between cord in an outermost narrow-width slant cord layer constituting the high-strength belt and cord in an innermost wide-width slant cord layer constituting the reinforcement belt.
In order to achieve the above object, the invention lies in a heavy duty radial tire comprising a radial carcass toroidally extending between a pair of bead cores embedded in respective bead portions, a tread rubber, a reinforcement belt comprised of at least one wide-width rubberized slant cord layer containing cords arranged obliquely with respect to an equatorial plane and a high-strength belt located inside the reinforcement belt in a radial direction of the tire and comprised of at least one narrow-width rubberized slant cord layer containing cords arranged obliquely with respect to the equatorial plane of the tire wherein the reinforcement belt and the high-strength belt are arranged between a crown portion of the radial carcass and the tread rubber and an intersect angle between cord in an innermost wide-width slant cord layer constituting the reinforcement belt and cord in an outermost narrow-width slant cord layer constituting the high-strength belt is not less than 10xc2x0 as measured at an acute angle side, characterized in that in a widthwise section of the tire when the tire is mounted onto an approved rim and inflated under a maximum air pressure corresponding to a maximum load capacity, the narrow-width slant cord layer constituting the high-strength belt has a width corresponding to 20xcx9c60% of a ground contact width of the tread rubber and an inclination cord angle of not more than 15xc2x0 with respect to the equatorial plane of the tire, and a rubber gauge of a first rubber layer located between the cord in the outermost wide-width slant cord layer and the cord in the innermost narrow-width slant cord layer is within a range of 0.9xcx9c3.0 times a diameter of the cord in the narrow-width slant cord layer.
The term xe2x80x9capproved rimxe2x80x9d used herein means an applied rim in a kind of tires, tire size and ply rating described in the following standard (xe2x80x9cApproved Rimxe2x80x9d, xe2x80x9cRecommended Rimxe2x80x9d), and the maximum load capacity and maximum air pressure adopt values described in the following standard.
That is, the standard is decided by an industrial standard effective in a zone manufacturing or using tires, which is, for example, xe2x80x9c1999 Year Bookxe2x80x9d of xe2x80x9cThe Tire and Rim Association Inc.xe2x80x9d in USA, xe2x80x9cStandard Manual 1999xe2x80x9d of xe2x80x9cThe European Tire and Rim Technical Organizationxe2x80x9d in Europe, and xe2x80x9cJATMA Year Book 1999xe2x80x9d of xe2x80x9cThe Japan Automobile Tire Manufacturers Association Inc.xe2x80x9d in Japan.
Further, the term xe2x80x9cwide-width slant cord layerxe2x80x9d used herein concretely means a slant cord layer having a width corresponding to 65xcx9c85% of a ground contact width of the tread rubber.
Moreover, the term xe2x80x9cground contact width of tread rubberxe2x80x9d used herein means a length of a line segment when the tire is mounted onto the approved rim and inflated under the maximum air pressure corresponding to the maximum load capacity and placed on a flat plate at a static state to determine ground contact end positions under a maximum load corresponding to the maximum load capacity and the ground contact end positions are connected along an axial direction of the tire at a state of turning no load.
Preferably, the high-strength belt has a lamination structure of two narrow-width slant cord layers, the cords of which layers being crossed with each other with respect to the equatorial plane, or is comprised of a single narrow-width slant cord layer.
And also, a rubber gauge of a second rubber layer located between ply cord located in the crown portion of the radial carcass and cord in the innermost narrow-width slant cord layer constituting the high-strength belt is within a range of 1.3xcx9c5.0 times a diameter of a cord in the narrow-width slant cord layer. In this way, the occurrence of separation failure between the radial carcass and the high-strength belt can more effectively be prevented to more improve the belt durability.
Moreover, the rubber gauges of the first rubber layer and the second rubber layer take values measured at the position on the equatorial plane of the tire.
In addition, it is preferable that the reinforcement belt has a cross cord layer comprised of two wide-width slant cord layers, the cords of which layers being crossed with each other with respect to the equatorial plane of the tire, that an inclination cord angle in the wide-width slant cord layers constituting the cross cord layer with respect to the equatorial plane of the tire is within a range of 10xcx9c40xc2x0, that rubber in the first rubber layer and the second rubber layer has a tensile stress at 100% elongation of 2.5xcx9c7.5 MPa, and that a protection layer comprised of a rubberized layer containing high-extensible cords arranged at an inclination angle of 15xcx9c40xc2x0 with respect to the equatorial plane of the tire is arranged between the tread rubber and the reinforcement belt so as to cover the full surface of the reinforcement belt.
Moreover, the xe2x80x9ctensile stress at 100% elongationxe2x80x9d is measured at room temperature according to a definition of JIS K6301.